AC/DC power converters including current transformers for bidirectional current sensing

ABSTRACT

An AC/DC power converter includes input terminals, output terminals, a power factor correction circuit coupled between the input and output terminals and including at least one power switch defining a switched current path, and a current transformer including a primary winding and a secondary winding. The primary winding is coupled in series with the switched current path. The power converter also includes a first sense switch coupled with a first end of the secondary winding, a second sense switch coupled with a second end of the secondary winding, and a control circuit. The control circuit is configured to turn on the first sense switch and turn off the second sense switch during a positive polarity of the AC voltage input, and to turn off the first sense switch and turn on the second sense switch during a negative polarity of the AC voltage input.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and priority to U.S. applicationSer. No. 16/841,034 filed Apr. 6, 2020. The entire disclosure of theabove application is incorporated herein by reference.

FIELD

The present disclosure relates to AC/DC power converters includingcurrent transformers for bidirectional current sensing.

BACKGROUND

This section provides background information related to the presentdisclosure which is not necessarily prior art.

AC/DC power converters may include circuit arrangement topologies wherecurrent through power switches changes direction during positive andnegative half cycles of an AC voltage input. Current transformers may beused to sense current through different portions of the power convertercircuit.

FIGS. 1A and 1B illustrate an example power converter 100 according tothe prior art. A primary winding P1 of a current transformer CT1 iscoupled in series with the power switches Q3 and Q4, and a single switchQ1 is coupled with the secondary winding S1 of the current transformerCT1.

A control circuit 101 is configured to turn on and turn off the switchQ1 according to a switching frequency of the power switches Q3 and Q4(e.g., a PWM signal with a kHz frequency, etc.). The control circuit 101may receive a sensed current of the power switches Q3 and Q4 at a node112 coupled between the switch Q1 and the resistor R1. This circuitarrangement may provide drawbacks, such as voltage spikes on theresistor R1 due to charging and discharging cycles at the gate of theswitch Q1 as the switch Q1 is turned on and off according to an ACswitching frequency of the power switches Q3 and Q4 (e.g., to allow thetransformer CT1 to reset, etc.).

FIG. 2 illustrates a transformer secondary side current sensing circuithaving a single switch Q1, according to the prior art. As shown in FIG.2 , the switch Q1 is not coupled between the resistor R1 and the currenttransformer TX1, to reduce voltage spikes on the resistor R1. A controlcircuit may sense current of the primary side power switches at the node212.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

According to one aspect of the present disclosure, an AC/DC powerconverter includes a pair of input terminals for receiving analternating current (AC) voltage input from an input power source, apair of output terminals for supplying a direct current (DC) voltageoutput to a load, and a power factor correction circuit coupled betweenthe pair of input terminals and the pair of output terminals. The powerfactor correction circuit includes at least one power switch defining aswitched current path. The power converter includes a currenttransformer having a primary winding and a secondary winding. Theprimary winding is coupled in series with the switched current path, andthe secondary winding includes a first end and a second end opposite thefirst end. The power converter also includes a bridge rectifier coupledwith the first and second ends of the secondary winding, a first senseswitch coupled with the bridge rectifier, and a second sense switchcoupled with the bridge rectifier. The control circuit is configured toturn on the first sense switch and turn off the second sense switchduring a positive polarity of the AC voltage input, and to turn off thefirst sense switch and turn on the second sense switch during a negativepolarity of the AC voltage input.

According to another aspect of the present disclosure, a bidirectionalcurrent sensing circuit for an AC/DC power converter includes a currenttransformer including a primary winding and a secondary winding. Theprimary winding is coupled in series with a switched current path of theAC/DC power converter. The circuit also includes a bridge rectifiercoupled with the secondary winding, a first sense switch and a secondsense switch each coupled with the bridge rectifier, and a controlcircuit configured to turn on the first sense switch and turn off thesecond sense switch during a positive polarity of an AC voltage input ofthe AC/DC power converter, and to turn off the first sense switch andturn on the second sense switch during a negative polarity of the ACvoltage input.

Further aspects and areas of applicability will become apparent from thedescription provided herein. It should be understood that variousaspects of this disclosure may be implemented individually or incombination with one or more other aspects. It should also be understoodthat the description and specific examples herein are intended forpurposes of illustration only and are not intended to limit the scope ofthe present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIGS. 1A and 1B are circuit diagrams of an AC/DC power converterincluding one current sense switch, according to the prior art.

FIG. 2 is a circuit diagram of another current transformer secondaryside circuit, according to the prior art.

FIGS. 3A and 3B are circuit diagrams of an AC/DC power converter,according to one example embodiment of the present disclosure.

FIG. 4 is a circuit diagram of an example current path through atransformer secondary side circuit of FIG. 3B during a positive AC inputpolarity.

FIG. 5 is a circuit diagram of an example current path through thetransformer secondary side circuit of FIG. 3B during a negative AC inputpolarity.

FIGS. 6A and 6B are circuit diagrams of an AC/DC power converterincluding two current transformers, according to another exampleembodiment of the present disclosure.

FIGS. 7A and 7B are circuit diagrams of an AC/DC power converterincluding two current transformers and a sense resistor, according toyet another example embodiment of the present disclosure.

FIG. 7C is a circuit diagram of a drive circuit for a switch of thetransformer secondary side circuit of FIG. 7B, according to anotherexample embodiment of the present disclosure.

FIG. 8 is a circuit diagram of a totem pole power factor correctionpower (PFC) converter, according to an example embodiment of the presentdisclosure.

FIG. 9 is a circuit diagram of a current sense circuit of the powerconverter of FIG. 8 .

FIG. 10 is a graph of example control signals and voltage waveforms ofthe power converter of FIG. 8 .

FIG. 11 is a circuit diagram of a Vienna rectifier circuit arrangement,according to an example embodiment of the present disclosure.

FIG. 12 is a circuit diagram of a current sense circuit including twocurrent sense switches, according to yet another example embodiment ofthe present disclosure.

FIG. 13 is a block diagram of an example control circuit for the powerconverter of FIGS. 3A and 3B.

FIG. 14 is a block diagram of an example analog control circuit for thepower converter of FIGS. 3A and 3B.

FIG. 15 is an example circuit diagram of the analog control circuit ofFIG. 14 .

FIG. 16 is a block diagram of an example digital signal processor (DSP)controller, according to another example embodiment of the presentdisclosure.

FIG. 17 is a block diagram of an analog control circuit, according toanother example embodiment of the present disclosure.

Corresponding reference numerals indicate corresponding parts orfeatures throughout the several views of the drawings.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference tothe accompanying drawings.

Example embodiments are provided so that this disclosure will bethorough, and will fully convey the scope to those who are skilled inthe art. Numerous specific details are set forth such as examples ofspecific components, devices, and methods, to provide a thoroughunderstanding of embodiments of the present disclosure. It will beapparent to those skilled in the art that specific details need not beemployed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. The method steps, processes, and operations described hereinare not to be construed as necessarily requiring their performance inthe particular order discussed or illustrated, unless specificallyidentified as an order of performance. It is also to be understood thatadditional or alternative steps may be employed.

Although the terms first, second, third, etc. may be used herein todescribe various elements, components, regions, layers and/or sections,these elements, components, regions, layers and/or sections should notbe limited by these terms. These terms may be only used to distinguishone element, component, region, layer or section from another region,layer or section. Terms such as “first,” “second,” and other numericalterms when used herein do not imply a sequence or order unless clearlyindicated by the context. Thus, a first element, component, region,layer or section discussed below could be termed a second element,component, region, layer or section without departing from the teachingsof the example embodiments.

Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,”“lower,” “above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. Spatiallyrelative terms may be intended to encompass different orientations ofthe device in use or operation in addition to the orientation depictedin the figures. For example, if the device in the figures is turnedover, elements described as “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the example term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein interpreted accordingly.

An AC/DC power converter according to one example embodiment of thepresent disclosure is illustrated in FIGS. 3A and 3B, and indicatedgenerally by reference number 300. The power supply 300 includes a pairof input terminals 302 and 304 for receiving an alternating current (AC)voltage input V1 from an input power source AC1, and a pair of outputterminals 306 and 308 for supplying a direct current (DC) voltage outputto a load.

As shown in FIG. 3A, power switches Q3 and Q4 are coupled in abridgeless power factor correction (PFC) circuit between the pair ofinput terminals 302, 304 and the pair of output terminals 306, 308. Thepower switches Q3 and Q4 define a switched current path. A currenttransformer CT1 includes a primary winding P1 and a secondary windingS1. The primary winding P1 is coupled in series with the switchedcurrent path defined by the power switches Q3 and Q4.

FIG. 3A illustrates the location of the current transformer CT1 relativeto the power switches Q3 and Q4, while FIG. 3B illustrates details ofthe current sense circuit coupled with the secondary winding S1 of thecurrent transformer CT1. As shown in FIG. 3B, the power converter 300includes a bridge rectifier having diodes D1, D2, D3 and D4 coupled withopposite ends of the secondary winding S1. A switch Q1 is coupled withthe diode D1, and a switch Q2 is coupled with the diode D2.

A control circuit 301 supplies a control signal A to the switch Q1 and acontrol signal B to the switch Q2. The control circuit 301 is configuredto turn on the switch Q1 and turn off the switch Q2 during a positivepolarity of the AC voltage input V1, and to turn off the switch Q1 andturn on the switch Q2 during a negative polarity of the AC voltage inputV1.

For example, the AC voltage input V1 may alternate between the positivepolarity and the negative polarity at a line frequency (e.g., aboutsixty Hertz, less than 1 kHz, etc.). The control circuit may beconfigured to turn on and turn off the switches Q1 and Q2 according tothe line frequency (e.g., in synchronization with the line frequency,etc.).

The control circuit 301 may include any suitable microprocessor,microcontroller, integrated circuit, digital signal processor,continuous conduction mode (CCM) power factor correction (PFC)controller, boundary conduction mode (BCM) PFC controller, etc., whichmay include memory. The control circuit 301 may be configured to perform(e.g., operable to perform, etc.) any of the example processes describedherein using any suitable hardware and/or software implementation. Forexample, the control circuit 301 may execute computer-executableinstructions stored in a memory, may include one or more logic gates,control circuitry, etc. voltages as described above.

A single control circuit 301 may control the power switches Q3 and Q4,and the secondary side circuit switches Q1 and Q2. In some embodiments,different control circuits may be used for the power switches Q3 and Q4,and the secondary side circuit switches Q1 and Q2. The control circuit301 may be the same as the control circuit 101 of FIG. 1 , or may be adifferent control circuit.

FIGS. 4 and 5 illustrate example current paths through the currenttransformer CT1 and the switches Q1 and Q2 during positive and negativehalf cycles of the AC voltage input V1. Specifically, FIG. 4 illustratesthat during the positive half cycle, the current flows from thesecondary winding S1 of the current transformer CT1, through the diodeD1 and the switch Q1 (which is turned on during the positive half cyclevia the control signal A), and through the resistor R1 (e.g., a burdenresistor) to a circuit ground 110. The current returns from the circuitground 310 to the secondary winding S1 via the diode D4.

FIG. 5 illustrates that during the negative half cycle, the currentflows from the untapped secondary winding S1 of the current transformerCT1, through the diode D2 and the switch Q2 (which is turned on duringthe negative half cycle via the control signal B), and through theresistor R1 to the circuit ground 310. The current returns from thecircuit ground 310 to the secondary winding S1 via the diode D3.

As shown in FIGS. 4 and 5 , the secondary winding S1 of the currenttransformer CT1 is preferably untapped, and is therefore notcenter-tapped, does not include any taps after a bifilar winding, and isnot coupled in series with any other secondary winding of the currenttransformer CT1.

The arrangement of the current transformer CT1 and the switches Q1 andQ2 allow for bidirectional current sensing (e.g., of current through theswitches Q3 and Q4), in a simple and cost-effective manner. For example,a current sense signal may be supplied to the control circuit at node312 (e.g., a node between the switches Q1 and Q2 and the resistor R1).

As shown in FIG. 3B, during a positive half cycle the switch Q1 may beturned on to detect current in the positive direction as the switches Q3and Q4 are turned on and turned off according to a switching frequency(e.g., according to a pulse-width modulated (PWM) signal, etc.), andduring a negative half cycle the switch Q2 may be turned on to detectcurrent in the negative direction as the switches Q3 and Q4 are turnedon and turned off according to the switching frequency.

As mentioned above, the switches Q1 and Q2 may be switched according tothe line frequency of the AC voltage input V1, and may be switched whenthe AC voltage input V1 is near or at zero (e.g., within one volt ofzero, within five percent of zero relative to a maximum value of V1,etc.). For example, the switches Q1 and Q2 may be switched as thevoltage of the AC voltage input V1 crosses zero, according to thepolarity change of the AC voltage input V1 as it crosses zero. A simplecontrol circuit (e.g., a microcontroller, a digital signal processor(DSP), a discrete logic circuit, etc.) may be used because the turn onand turn off timing of the switches Q1 and Q2 may be less critical thatif the switches Q1 and Q2 were switched at a higher frequency onnon-zero voltages.

Using two switches Q1 and Q2 avoids the need to turn on and turn off aswitch at the same switching frequency as the switches Q3 and Q4, andmay avoid voltage spikes on the resistor R1 that could otherwise occurif only a single switch were used instead of the switches Q1 and Q2(e.g., due to gate charging and discharging if a switch were turned onand off at the switching frequency to allow the current transformer CT1to reset, etc.).

As shown in FIGS. 3A and 3B, the power converter 300 includes twoinductors L1 and L2 coupled with the AC voltage input V1, and fourdiodes D5, D6, D7 and D8 coupled with the inductors L1 and L2. Acapacitor C1 is coupled with the diodes D5-D8 and across the outputterminals 306, 308.

The power converter 300 also includes zener diodes D9 and D10 coupledwith the secondary winding S1 of the current transformer CT1. The zenerdiodes D9 and D10 clamp a reset voltage spike of the bi-directionalcurrent transformer CT1 if the voltage spike exceeds the zener rating,to protect the switches Q1 and Q2 and the diodes D1-D4. Although FIG. 3Billustrates the zener diode D9 coupled with one end of the secondarywinding S1 and the zener diode D10 coupled with another end of thesecondary winding S1, other embodiments may use more or less (or none)of the zener diodes, zener diodes located in other arrangements, etc.For example, the two zener diodes may be connected in series between thecathode of the diode D2 and the circuit ground 310.

In other embodiments, the power converter 300 may include more or lessdiodes, switches, capacitors and/or inductors. The power converter 300may include diodes, switches, capacitors and/or inductors coupled inother circuit arrangements (which may or may not be bridgeless), such astotem pole PFCs, Vienna rectifiers, etc. In some embodiments, thecurrent transformer sensing circuits may be used in other bidirectionalcurrent sensing applications, such as motor control circuits, DC/ACpower inverters including solar inverters, etc.

The switches Q1-Q4 may include any suitable switching devices, such asbipolar-junction switch (BJTs), metal-oxide semiconductor field-effecttransistors (MOSFETs), Silicon (Si) transistors, etc. The inputterminals 302, 304 and output terminals 306, 308 may include anysuitable connectors, wires, leads, etc. for transferring power to andfrom the power converter 300. The current transformer CT1 may includeany suitable transformer for sensing current, and may include anysuitable number of windings, layers, wire type, core construction, etc.

FIGS. 6A and 6B illustrate an AC/DC bridgeless power converter 400according to another example embodiment of the present disclosure. Thepower converter 400 includes a current transformer CT1 in series withpower switches Q3 and Q4, and another current transformer CT2 having aprimary winding P2 coupled between the inductor L1 and the diode D13.The diodes D13, D14, D15 and D16 are connected between the AC voltageinput V1 and the capacitor C1. Although FIG. 6B illustrates the currenttransformer CT2 coupled with a diode D13, in other embodiments thecurrent transformer CT2 may be coupled with a transistor, such as aMOSFET (e.g., an SiC MOSFET, a GaN transistor, etc.).

FIG. 6A illustrates the location of the current transformers CT1 and CT2with respect to the inductor L1 and the power switches Q1 and Q2, whileFIG. 6B illustrates the details of the current sense circuit connectedwith the secondary windings S1 and S2 of the current transformers CT1and CT2.

For example, the switches Q1 and Q2 are coupled to nodes between thesecondary windings of the current transformers CT1, CT2. A controlcircuit receives a sensed current signal at 412 that is indicative of atotal current of the inductor L1. FIG. 10 illustrates an example outputwaveform 1003 of the sensed current signal at 412 during operation ofthe power converter 400. Specifically, the current transformer CT1 maysense the current though the power switches Q3 and Q4, while the currenttransformer CT2 senses the current through the diode D1. A combinationof the currents may provide a total current of the inductor L1.

As shown in FIG. 6B, zener diodes D7 and D8 are coupled between oppositeends of the secondary winding S1 of the current transformer CT2, anddiodes D9 and D10 are coupled between opposite ends of the secondarywinding S1 of the current transformer CT1. The diodes D3 and D4 connectopposite ends of the secondary winding S1 of the current transformer CT1to the circuit ground 410, and the diodes D5 and D6 connect oppositeends of the secondary winding S1 of the current transformer CT2 to thecircuit ground 410.

The diodes D1, D2, D11 and D12 are coupled between the currenttransformers CT1 and CT2, and the switches Q1 and Q2. Although FIG. 6Billustrates one specific arrangement of the diodes, switches andresistor in the current sensing portion of the power converter 600,other embodiments may include other arrangements of the components.

For example, FIGS. 7A and 7B illustrate a power converter 500 accordingto another example embodiment of the present disclosure, where theswitches Q1 and Q2 are not coupled between the resistor R1 and thecurrent transformers CT1 and CT2.

In the power converter 500, the resistor R1 is coupled between thecircuit ground 510 and a node located between the diodes D1, D2, D11 andD12. A control circuit may receive a sensed current at the node 512 thatis indicative of the total current of the inductor L1.

As shown in FIG. 7B, a diode D3 is coupled between the currenttransformer CT1 and the switch Q1, a diode D4 is coupled between thecurrent transformer CT1 and the switch Q3, a diode D5 is coupled betweenthe current transformer CT2 and the switch Q1, and a diode D6 is coupledbetween the current transformer CT2 and the switch Q3.

FIG. 7C illustrates a drive circuit for the switch Q1, which may be ap-channel FET (e.g., a p-channel MOSFET may be used in the bottom sideof the current transformer rectifier bridge). The drive circuit includesa diode D4, a capacitor C1 and a resistor R2, and may be configured toturn on and turn off the switch Q1 at a switching frequency that is thesame as power switches of the power converter.

FIG. 8 illustrates an AC/DC bridgeless power converter 400 that includesa totem pole power factor correction (PFC) circuit arrangement. As shownin FIG. 8 , the power converter 600 includes an electromagneticinterference (EMI) filter 614 that receives an AC voltage input fromphase and neutral terminals. The EMI filter 614 is connected with aprotective earth ground P.E.

The EMI filter 614 supplies line (EMI_L) and neutral (EMI_N) to a boostinductor L1. The switches Q3, Q4, Q5 and Q6 are connected in a totempole circuit arrangement and driven by a control circuit includingisolated drivers 616. The switches Q3-Q6 may include any suitableswitches, such as GaN metal-oxide semiconductor field-effect transistors(MOSFETs), etc. A bulk capacitor C1 supplies an output voltage to theoutput terminals Bulk_+Ve and Bulk_−Ve.

A first current transformer CT1 is coupled in series with the switch Q5and a second current transformer CT2 is coupled in series with theswitch Q6. FIG. 9 illustrates an example current sensing circuit coupledbetween the current transformers CT1 and CT2 in the power converter 400.

For example, the circuit in FIG. 9 may be similar to the circuit of FIG.6B. As shown in FIG. 9 , the switches Q1 and Q2 are coupled between theresistor R1 and the secondary windings of the current transformers CT1and CT2. The switches Q1 and Q2 may be switched at the line frequencyvia the control signals A and B, and a control circuit may measure abidirectional total current of the inductor at a node 612.

FIG. 10 illustrates example control signals and current waveforms forthe power converter 600 of FIGS. 8 and 9 . As shown in FIG. 10 , duringa positive half cycle of the AC input voltage, a control signal A to aFET coupled with the current transformer CT1 and a control signal A to aFET coupled with the current transformer CT2 may be both be high, whilethe control signals B are low.

Conversely, during a negative half cycle of the AC input voltage, thecontrol signal B to another FET coupled with the current transformer CT1and the control signal B to another FET coupled with the currenttransformer CT2 may be both be high, while the control signals A arelow. Because the FETs for both current transformers CT1 and CT2 would beswitched identically, a single set of switches Q1 and Q2 may be used forboth of the current transformers CT1 and CT2 in FIG. 9 .

In some embodiments, the same control switch(es) may be used for a powerswitch current transformer sensing and power diode or switch sidecurrent sensing. This may be particularly advantageous in an interleavedpower stage configuration where one or more of the current return pathsis shared by both power stages and the current transformer position isrestricted by the circuit arrangement.

FIG. 11 illustrates a power converter 700 that includes a Viennarectifier circuit. As shown in FIG. 11 , the power converter 700includes three phase legs PH_1, PH_2 and PH_3. The phase leg PH_1includes a voltage source V1, and a current transformer CT1 in serieswith a power switch S1.

The phase leg PH_2 includes a voltage source V2, and a currenttransformer CT2 in series with a power switch S2, and the phase leg PH_3includes a voltage source V3, and a current transformer CT3 in serieswith a power switch S3.

Each current transformer CT1, CT2 and CT3 may sense bidirectionalcurrent in its corresponding phase leg PH_1, PH_2 or PH_3. For example,a secondary side circuit of each current transformer CT1, CT2 and CT3may be similar to the circuit of FIG. 3B, the circuit of FIG. 12 , etc.A control signal for switches in the secondary side circuits may begenerated by sensing individual phase voltages with respect to theBulk_Return node, and a DSP, microprocessor, etc. may be used to detectpolarity of the individual phases.

As shown in FIG. 11 , the power converter 700 includes diodes D1, D2,D3, D4, D5 and D6 coupled between corresponding inductors L1, L2 or L3,and the output nodes +Ve_Bulk and −Ve_Bulk. The capacitors C1 and C2 arecoupled between the node Bulk_Return a corresponding one of the outputnodes +Ve_Bulk and −Ve_Bulk. In other embodiments, the power converter700 may use other Vienna rectifier circuit arrangements, including moreor less circuit components.

FIG. 12 illustrates a current sense circuit 800 including two switchesQ1 and Q2, according to another example embodiment of the presentdisclosure. As shown in FIG. 12 , the switches Q1 and Q2 are not coupledbetween the resistor R1 and the current transformer CT1. A controlcircuit may receive a sensed current at the node 812.

FIGS. 13-15 illustrate example control circuit configurations for thepower converters described herein. For example, as shown in FIG. 13 , apower converter 900 may include an AC voltage divider 918 and a digitalcontroller 920 (e.g., a microcontroller, a digital signal processor(DSP), etc.). The digital controller 920 may already be able to performand/or detect polarity information, zero-crossing information, etc., ofan AC input.

FIG. 14 illustrates an example analog control circuit 1000 including anAC voltage divider 1018 and a polarity detection comparator 1022. Forexample, FIG. 15 illustrates an analog circuit 1100 where the resistorsR1, R2, R3 and R4 are connected with a LIVE terminal, and the resistorsR5, R6, R7 and R8 are connected with the NEUTRAL terminal. A comparatorX1 receives the voltage divider output and supplies a signal V_OUT,which uses hysteresis and a voltage supply V2.

FIG. 16 illustrates an example control circuit 1201, according toanother example embodiment of the present disclosure. The controlcircuit 1201 includes a digital signal processor (DSP) 1203, which maybe used to control one more switches of a power converter. For example,the output signal PWM may be a pulse width modulation signal thatcontrols switching of the switches Q3 and Q4 of the power converter 300of FIG. 3A, etc.

The Vin_rect signal may be fed to two separate analog to digital (ADC)pins, to generate a difference inside the DSP 1203 for computation andcontrol. For example, the DSP 1203 includes a peak detector that outputsa Vmax value to a 1/Vmax{circumflex over ( )}2 block, which ismultiplied with a signal from the ADCVin block that receives the signalVin_rect.

The output bulk voltage Vo is received at the block ADCVo to providefeedback for voltage loop control. The output voltage is sent to aovervoltage protection block OVP, and also to a voltage compensator thatdetermines a difference between the output voltage and a voltagereference Vref, and multiples with the input Vin_rect after a gain isapplied at the block GV(s).

A current signal iL represents the current feedback information sensedfrom the current transformer (e.g., via the node 312 if FIG. 3B), forcurrent loop control, and overcurrent protection via the block OCP. Forexample, the output of the combined Vin and Vo signals may provide acurrent reference Iref, and a difference between the sensed signal iLand the current reference Iref may be used to the PWM signal via a gainlock Gi(s) and the block DPWM.

FIG. 17 illustrates an analog control circuit 1301 for secondary sensingcircuit switches (such as the switches Q1 and Q2 in the power converter300 of FIG. 3B), according to another example embodiment of the presentdisclosure. The circuit 1301 receives input AC_Line and AC_Neutral(which may be sensed after a voltage divider, etc.), and compares theinputs using a comparator X1.

An output of the comparator X1 may be fed back to a microcontroller,etc., and the output may drive the switch Q5 via a resistor R6. Thenodes VCC(A) and VCC(B) provide supply voltages for the comparator X1and the switches Q5 and Q6. The gate of the switch Q6 is coupled to thedrain of the switch Q5, so the switches Q5 and Q6 are alternatelyswitched.

The circuit 1301 outputs a signal Q1 Drive to drive a switch Q1 of thesecondary side sensing circuit (e.g., the switch Q1 of FIG. 3B), and thecircuit 1301 outputs a signal Q2 Drive to drive a switch Q2 of thesecondary side sensing circuit (e.g., the switch Q2 of FIG. 3B).Therefore, the circuit 1301 may alternately turn on and turn off theswitches Q1 and Q2 according to a polarity of the AC voltage input,where the turn on and turn off events occur at a zero crossing of the ACvoltage input.

The circuit 1301 includes three capacitors C1, C2 and C3, as well as sixother resistors R2, R3, R4, R5, R7 and R8. In other embodiments, thecircuit 1301 may include any other suitable arrangement of circuitcomponents.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

The invention claimed is:
 1. A bidirectional current sensing circuit foran AC/DC power converter, the circuit comprising: a first currenttransformer comprising: a primary winding coupled in series with a firstcurrent path of the AC/DC power converter; and a secondary winding; afirst rectifier assembly coupled with the secondary winding of the firstcurrent transformer; a second current transformer comprising: a primarywinding coupled in series with a second current path of the AC/DC powerconverter; and a secondary winding; a second rectifier assembly coupledwith the secondary winding of the second current transformer; a firstsense switch coupled with the first and second rectifier assemblies; asecond sense switch coupled with the first and second rectifierassemblies; a control circuit configured to: turn on the first senseswitch during a positive polarity of an AC voltage input of the AC/DCpower converter to provide a first current path for both of the firstand second rectifier assemblies; and turn on the second sense switchduring a negative polarity of the AC voltage input to provide a secondcurrent path for both of the first and second rectifier assemblies. 2.The bidirectional current sensing circuit of claim 1, wherein thecontrol circuit is further configured to: turn off the second senseswitch during the positive polarity of the AC voltage input; and turnoff the first sense switch during the negative polarity of the ACvoltage input.
 3. The bidirectional current sensing circuit of claim 1,wherein the secondary winding of the first current transformer comprisesan untapped secondary winding that is not coupled in series with anyother secondary winding of the first current transformer.
 4. Thebidirectional current sensing circuit of claim 1, wherein the firstcurrent path of the AC/DC power converter comprises a switched currentpath.
 5. The bidirectional current sensing circuit of claim 1, whereinthe control circuit is configured to turn on and turn off the first andsecond sense switches in synchronization with a line frequency of the ACvoltage input and according to the polarity of the AC voltage input. 6.The bidirectional current sensing circuit of claim 1, wherein thecontrol circuit is configured to turn on and turn off the first andsecond sense switches in response to a voltage of the AC voltage inputcrossing zero.
 7. The bidirectional current sensing circuit of claim 1further comprising a sense resistor, wherein: the first sense switch iscoupled with the second sense switch via a circuit node; the senseresistor is coupled between the circuit node and a circuit ground; andthe control circuit is coupled with the circuit node and configured todetect a bidirectional current of the at least one power switch.
 8. Thebidirectional current sensing circuit of claim 1, wherein: a first endof the first sense switch is coupled with a first end of the secondsense switch via a circuit node; the circuit node is coupled to acircuit ground; a second end of the first sense switch is coupled with afirst diode of the first rectifier assembly and with a first diode ofthe second rectifier assembly; and a second end of the second senseswitch is coupled with a second diode of the first rectifier assemblyand with a second diode of the second rectifier assembly.
 9. A method ofmanufacturing a power converter comprising: coupling a first currenttransformer to a first power switch of a switched current path of apower factor correction circuit, the first current transformercomprising: a primary winding coupled in series with the first powerswitch; and a secondary winding; coupling a first bridge rectifier withthe secondary winding of the first current transformer; coupling asecond current transformer to the first current transformer, the secondcurrent transformer comprising: a primary winding coupled to the primarywinding of the first current transformer; and a secondary winding;coupling a second bridge rectifier with the secondary winding of thesecond current transformer; coupling a first sense switch with the firstand second rectifier assemblies; coupling a second sense switch with thefirst and second rectifier assemblies; turning on the first sense switchto create a first path to a circuit ground for each of the first andsecond rectifier assemblies; and turning on the second sense switch tocreate a second path to the circuit ground for each of the first andsecond rectifier assemblies.
 10. The method of claim 9 furthercomprising: coupling a control circuit with the first and second senseswitches; and configuring the control circuit to: turn on the firstsense switch during a positive polarity of an AC voltage input into thepower factor correction circuit; and turn on the second sense switchduring a negative polarity of the AC voltage.
 11. The method of claim 10further comprising configuring the control circuit to turn the first andsecond sense switches on and off in synchronization with a linefrequency of the AC voltage and according to the polarity of the ACvoltage.
 12. The method of claim 11 further comprising configuring thecontrol circuit to turn the first and second sense switches on and offin response to the AC voltage crossing zero.
 13. The method of claim 10further comprising: coupling a sense resistor to the first sense switchvia a circuit node; coupling the sense resistor to the second senseswitch via the circuit node; and coupling the sense resistor to thecircuit ground, the sense resistor positioned between the circuit nodeand the circuit ground.
 14. The method of claim 13 further comprising:coupling the control circuit to the circuit node; and configuring thecontrol circuit to detect a bidirectional current of the first powerswitch via the sense resistor.
 15. The method of claim 10 furthercomprising configuring the control circuit to: turn off the second senseswitch during the positive polarity of the AC voltage input; and turnoff the first sense switch during the negative polarity of the ACvoltage input.
 16. A method of converting AC power to DC powercomprising: controlling at least one switch of a power factor correctioncircuit according to a switching frequency to generate a current in aswitched current path of the power factor correction circuit;controlling a first current sense switch into an on state to: generate,via a first current transformer, a first sensing current in a firstrectifier assembly; and generate, via a second current transformer, asecond sensing current in a second rectifier assembly; controlling asecond current sense switch into the on state to: generate, via thefirst current transformer, a third sensing current in the firstrectifier assembly; and generate, via the second current transformer, afourth sensing current in the second rectifier assembly.
 17. The methodof claim 16, further comprising: receiving an AC voltage via a pair ofinput terminals; detecting, via a control circuit, a voltage polarity ofthe AC voltage; and wherein, in response to the voltage polarity being apositive polarity: controlling the first current sense switch comprisescontrolling the first current sense switch into the on state; andcontrolling the second current sense switch comprises controlling thesecond current sense switch into an off state.
 18. The method of claim17, wherein, in response to the voltage polarity being a negativepolarity: controlling the first current sense switch comprisescontrolling the first current sense switch into the off state; andcontrolling the second current sense switch comprises controlling thesecond current sense switch into the on state.
 19. The method of claim16 further comprising detecting at least one of the first, second,third, and fourth sensing currents flowing through a sense resistorcoupled to the first and second current sense switches.
 20. The methodof claim 19, wherein the first, second, third, and fourth sensingcurrents are included in secondary windings of the first and secondcurrent transformers via primary windings of the first and secondcurrent transformers in response to controlling the at least one switchof the power factor correction circuit according to the switchingfrequency.